It is often convenient to enable voice communications without requiring the use of a handset or headset to locate a microphone adjacent the mouth of a user and a speaker adjacent an ear of the user. Accordingly, speaker phones using broadcast speakers in combination with far talk microphones are available. However, conventional speaker phones are disruptive when used in open or cubical type office floor plans. In addition, it is often impossible to have a private conversation using a speaker phone in an office environment.
Conventional speaker phones also have limitations when used in connection with group conference calls. In particular, because speaker phones broadcast their output, it is impossible for individual participants at a location to independently control the volume of the sound. In addition, the broadcasting of output prevents different participants at a location from receiving different audio streams. For example, broadcasting a version of the output in a first language while at the same time broadcasting a version of the output in one or more additional languages results in high ambient noise levels and would be generally unintelligible due to the multiple different audio sources. Furthermore, the use of one or more conventional speakers to broadcast an output results in only a limited ability to provide spatial information, which can be used to assist listeners in identifying the source of audible information being received (e.g., to identify the person speaking).
In addition, conventional speaker phones used in combination with far talk microphones can result in the creation of echoes in a transmitted signal. In particular, a microphone provided in connection with a conventional speaker phone receives the output from the speaker, as well as signals provided by the user or users of the speaker phone. Accordingly, conventional speaker phones must prevent or cancel echoes created by the reception of speaker output by the microphone. For example, speaker phones may incorporate digital signal processors operating to remove echoes from transmitted voice signals. Another existing technique to avoid echo is to switch a half duplex channel between transmission and reception based on the voice activity detected at each end. This technique generally reduces voice quality and conference interaction through introducing artifacts such as speech clipping and difficulties associated with interrupting the current talker. However, the use of digital signal processors increases the cost of the speaker phone. Conventional speaker phones may also avoid echoes by providing directional microphones. However, directional microphones are expensive, and are ineffective in certain circumstances, such as when a speaker is moving about the room.
In order to provide spatial information, techniques utilizing multiple audio channels have been developed. Although such techniques are promising in connection with home theaters and computer game applications, the listener's ears must be located within a narrowly defined sweet spot. In addition, the orientation of the listener influences the accuracy with which spatial information is provided. Because the sweet spot encompasses a restricted area, and because the orientation of the listener must be known, such techniques are not particularly useful in connection with a conference call scenario in which participants sit around a speaker phone located in the middle of a table.
In order to provide a targeted source of sound, techniques that take advantage of the non-linear properties of air to create a narrow beam of sound have been developed. For example, parametric audio systems utilizing arrays of acoustic transducers are known. Such systems take advantage of the non-linear characteristics of air to create an audible signal from the interaction of ultrasonic signals and the air. Such systems have been successful in creating an audio source along an audio path defined by ultrasonic signals emitted by a parametric speaker. However, the advantages of such systems in connection with personalized conference and hands-free telephony has not heretofore been recognized or applied.